1. Field of the Invention
The present invention relates to a method of producing toner that is used to visualize the electrostatic latent image in image-forming methods such as electrophotographic methods, electrostatic recording methods, magnetic recording methods, and toner jet methods.
2. Description of the Related Art
The technology of visualizing image information through an electrostatic latent image, as in, for example, electrophotographic methods, is in wide use in a variety of fields, e.g., copiers, printers, and so forth. The fields of application have also broadened as technology has developed, and electrophotographic equipment has thus become quite diverse and there has been demand for various types of additional value, such as a higher image quality and improvements in the durability and fixing performance.
Against this background, segregated-functionality structures have in recent years become the favorite for the toners used in electrophotographic methods (devices), while the main stream in toner production has become wets, which can relatively easily provide additional value. Various systems have been investigated for wet toners by the individual companies, and production methods such as suspension polymerization methods, emulsion polymerization methods, and solution suspension methods have been suggested according to a function of the material composed in the toner and the desired toner particle morphology.
For example, in the suspension polymerization methods and solution suspension methods, a colorant-dispersed solution that constitutes the toner is granulated in a liquid dispersion medium using a high-speed stirrer to obtain liquid droplets that have a desired particle diameter. A toner particles-dispersed solution is then obtained, in suspension polymerization methods by carrying out a polymerization step and in solution suspension methods by removing the solvent. This is followed by separation of a cake of damp toner particles from the toner particles-dispersed solution and acquisition of the toner particles by pulverizing and drying. Classification is then performed as necessary and prescribed additives are added to produce the toner. A production method of this type facilitates the generation of a high durability in combination with a high developing performance and can provide a toner that has a segregated-functionality core-shell structure.
A toner with an improved fixing performance and an improved transfer performance, achieved by a more detailed engineering of the core-shell structure and specifying the microcompression hardness of the toner, has been disclosed (for example, Japanese Patent Application Laid-open No. 2008-145950).
A method has also been disclosed that makes possible a low-temperature fixability and an enhanced gloss without a loss of durability; this is achieved by controlling the molecular weight distribution of the core by the addition of a low-molecular weight component (for example, Japanese Patent Application Laid-open No. 2007-41503).
These methods make it possible to impart a desired functionality to toner and have resulted in very substantial improvements in performance. On the other hand, in order to provide electrophotographic devices that meet the growing demands imposed by the marketplace, it has become necessary to design toner in conformity to individual devices, which has made the production of multiple product types unavoidable. Due to this, a stability capable of withstanding even the long-term standing caused by product change over has also come to be required of the above-mentioned colorant-dispersed solution.
However, the conventional production methods have certain problems with regard to the long-term stability of the colorant-dispersed solution, and a problem here has been the occurrence to a greater or lesser degree of segregation of the material in the colorant-dispersed solution during long-term standing. Due to this, at the present time the problem arises that toner particles produced after long-term standing of the colorant-dispersed solution mixture exhibit a distorted or disturbed particle diameter distribution, which results in the problem of an inferior durability and developing performance.
In addition, the production process necessary to execute the segregated functionality mentioned above is more complex than in the past, and quiescence or stasis in the individual production steps can occur. In view of these circumstances, it is again a very important problem to bring about a stable colorant-dispersed solution mixture through an excellent state of dispersion.
The stable production of a plurality of toner product types is also still a problem to be addressed, and the appearance of a technology that provides a high degree of dispersion stabilization for colorant-dispersed solution mixtures is strongly desired.